I have read that there uis nothing that can be done to fix this flat spot between 3000 and 3700 RPM on the MCS. No tuning, no ECU massage, no mods, etc.

Does the MC also deal with this?
Is this a result of California emmissions software?

My Unichip can't seem to put a dent in it. But then I don't have a custom tune yet.

This is perplexing and shouldn't be there.

Paul

 

this didnt happen since you put in a enlarged TB?

 

I have been able to make minimal changes with a custom tune, but for the most part, there is an issue with the S. The interface between the throttle response and bypass valve is to blame.

Hope that helps!
Randy

 

Randy is correct, it is not a tuning issue. The mid 3000 RPM flat spot while in cruise mode (manifold vacuum, light engine load, low RPM) seems to be a function of intake port shape, fuel injector location, and the resulting inability to carry fuel. It is noticeable when you try to accelerate: you open the butterfly and mush. The Mini is not unique to this phenomenon: it has been studied for 40+ years on cars as varied as sprint cars to Civics. The only known solution, short of redesigning the intake ports, is to install a purpose built header such as Stahl has done.

 

No, my TB is only a 59mm so it's not the culprit, and yes it was there before I installed the TB.

But keep thinking. Maybe Randy and DMH have it pinned.

Paul

 

Really? Is this proven as yet, or can any header help? I've been quite interested in the header wars and when each company comes out with the latest and greatest I really kind of wonder.

I did look at the Stahl on your web site but would be interested in how it is able to fix this flat spot.

Tanks.
Paul

 

Paul: Actually Don has replied to this question, and others have contributed. I've read them all, and they make sense. Unfortunately I cannot repeat the arguments so I recommend to you that you seek the answers yourself. Or not. Trust me.

 

Header war? Correct me if I’m wrong but I don’t know of anyone selling a high performance header for the Mini other than me and Stahl. I sell an MTH header that is similar in design to the Milltek, Madness, Alta, and GTT to name a few but they are strictly for street applications and not high performance.

The header solution has been around for many decades; before fuel injection, in days of carburetion. This has been written about many times in books such as Internal Combustion Engine Fundamentalsby John Heywood. I really don’t think anybody knows why the header solution works; the knowledge built up is from decades of trial and error. It is also the cheaper solution to redesigning the intake port. But it is not as easy as installing any header; they have to be properly made to take into account the issue. You can’t just weld a round tube to the flange and call it a day; it has to be port shaped and properly sized (diameter and length).

If you have ever tried to follow the pace car under a yellow, then you know what is going on and that is why you try to clear the engine. It happens in NASCAR, Sprint Cars, Touring Cars, etc. Maybe direct injection will be the ultimate answer.

 

A question DMH,

If it is not a tuning issue, why would I not have had the flat-spot until after the ECU update that was for an emissions recall?

I am not saying that your theory about intake ports dosen't have value, but at one time my 02 MCS did not have the flat spot.

 

My guess is that you were less aware of it before the reflash. It's just now more pronounced. All of these cars have it; it is inherent in the design.

 

It's not often Randy is wrong, but in this case I've done the datalogging, and have found the reason for the flatspot. Randy's orginal UNIchip tunings are way off to try to help the flatspot, so I'm not suprized to see him write that minimal changes have minimal impact. The flatspot may be amplified by the port shapes and resonances, however the drivability can be dramatically smoothed out with some basic fuel and timing adjustments.

I have a hunch that anyone with GIAC doesn't have any of the factory flatspots....any GIAC customers out there that can verfiy my hunch?

 

To add a bit of info my car has a flat spot from 3000 to 3200 rpm. At that range by a/f mix goes from 14.5 ro 12.3 -12.5. I am running a 64mm tb and have a basic MTH map.

Randy
M7 Tuning

 

They may have just been covering up the hole with a bunch of gas (rich) or using timing tricks to make it less noticeable (note that reducing power before and after the hole can accomplish this). But given how variable the tolerances are in the MINI engine (I mean there are over 25hp differences between samples on the same dyno so you know it's not a real precision piece), that may have caused some examples to fail emissions, leading to the recall.

From a purely theoretical standpoint and if it is reversion in the intake, extremely long header primary tubes that are tuned for ~3500rpm should indeed help pull a larger fuel charge into the chamber during the overlap when both exhaust and intake valves are open. But this should also theoretically increase hydrocarbon emissions (though the MINI catalysts may have some excess capability since it always runs so rich anyway and they even frivolously programmed extra lift-throttle richness to produce the pop-pop sound in the '05+ models).

I am really looking forward to field reports of the Stahl header on drivability and CELs. In the meantime, if you have this problem of a bog when tipping into the gas at ~3500, may I suggest first trying the VGS mod and/or adjusting the BPV?

 

They do not work to correct this problem. It is not supercharge related.
No CELs so far!

 

Tried the VGS, switched to the BPV almost a year ago. Neither helped the flat-spot.

I have an OBX header that's not installed yet, but if the Stahl header actually did get rid of the flat-spot I would be very interested.

Is anyone doing a head that corrects the poor intake port design? Something not purely race but great for the street also. On the track, the flat-spot isn't an issue.

 

I would think that there would be a small percentage of MINI owners that are also regular track drivers in their cars.
Don't get me wrong, I recently had the time of my life going around Laguna Seca at speed (for short segments), it is a kick, but the far greatest amount of time in my vehicle is on public streets.
I just don't think there will be that many MINI owners wanting to deal with this flat spot will opt for this Stahl system.
Maybe I'm expecting too much here.

Paul

 

The OBX header will do nothing to improve the flat spot.
It's not only the head port shape but the intake manifold and injector location that adds to the problem. No one that I know is dealing with it that way however. It is typically addressed with a header.

 

I didn't have them built to only address the flat spot. I had them build because no one that I know of in the Mini community is building serious, high performance headers. In addition to the Stahl header I sell the MTH header but they, like the Madness, Alta, and GTT to name a few, are not designed for serious, high performance but rather are headers for street applications. They serve their purpose but I am looking in a different direction with the Stahl header. And the Stahl header is streetable.

 

Well, you may have me convinced.
I'll be very interested in the sound quality and quantity from the street style mufflers when they are ready to be tested. Also in what valance changes you have up your sleeve. They (stahl header and catback) do seem to be built with quality of workmanship in mind.

Paul

 

Apologies for resurrecting this thread but since I installed a 17% pulley about a month ago, I've noticed a flat spot from about 2600-3000rpm. At 3k the car takes off but, for instance, if I am cruising in 3rd and drop to around 2500rpm (let's say b/c of traffic) then try to accelerate quickly there is very little response from the engine. It'll kinda stumble to 3k and then get up and go.

Another example is when shifting from 1st to 2nd, if I shift at about 3300 when the transmission hooks up in second at ~2800 it'll stumble a little bit until it gets over 3k and then smooth out.

I am wondering if this is due to the inherent flat spot discussed in this thread or if it is something that can be dealt with via a tune (GIAC or MTH). Only mods to the engine are an Alta CAI and 17% pulley.

Any thoughts?

 

The flat spot is more pronounced with a 17% pulley -- you are making it leaner. Software would help but not totally eliminate it.

 

I too am interested in reports from a third party putting on the Stahl and reporting the findings...... this (flat spot) has been a problem since day 1.... and while I have minimized it over the years with different techniques.... I can't say it is gone.... very interested...

It is interesting that Mini has "known" about the problem and did not make a running change.....very curious......

 

The issue is not unique to the Mini and for street cars it does not present any real problem.
Another run of Stage 2 headers will be finished on Monday.

 

I'm curious Don if the new Wegerner (sp?) head is ported correctly to eliminate the problem

 

I am as well, but the $$$$ toll is really adding up here, what with the M62 and the Stahl system, and then the Wegerner head.

That's about $8K!!!!

YIPES :impatient

Oh well.

Paul